<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>
    <button id='btn'>发送Ajax请求</button>
    <script>
        var btn = document.getElementById('btn');
        btn.onclick = function () {
            var xhr = new XMLHttpRequest();
            xhr.open('get', 'http://localhost:3000/cache?t=' + Math.random());
            xhr.send();
            xhr.onreadystatechange = function () {
                if (xhr.readyState == 4 && xhr.status == 200) {
                    alert(xhr.responseText);
                }
            }

        }
    </script>
</body>

</html>